Chapter 21. Diuretic Agents. Mosby items and derived items 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.

Transcription

1 Chapter 21 Diuretic Agents

2 Renal Structure and Function Kidneys at level of umbilicus Each weighs 160 to 175 g and is 10 to 12 cm long Most blood flow per gram of weight in body 22% of cardiac output (CO) Active organ (not a passive filter)

3 Renal Structure and Function (cont d) Nephron is functional unit (maintains homeostasis of internal volume/electrolytes) Glomerulus Proximal tubule Loop of Henle Distal tubule Collecting duct

4 Renal Structure and Function Glomerular filtration (cont d) 20% of total blood flow through nephron 99% reabsorbed in tubules 1% excreted as urine Adult output = 30 to 60 ml/hr Diuretics increase urine output by interfering with reabsorption in tubules

5 Renal Structure and Function (cont d) Electrolyte filtration and reabsorption Na: 70% is reabsorbed in proximal tubules, 20% in loops of Henle, 10% in distal tubules Inhibition causes less H 2 O retention K: Reabsorbed mostly in proximal tubules Cl and HCO 3- : Passively reabsorbed in tubules Aldosterone: Increases Na and H 2 O reabsorption in distal tubule

6 Renal Structure and Function Acid-base balance (cont d) May be caused by H 2 O loss Na reabsorption With Cl to preserve neutrality Exchange of Na for H or K Low Cl or K = metabolic alkalosis Loss of HCO 3- buffer = metabolic acidosis

7 Diuretic Groups Osmotic diuretics Impair proximal tubule and ascending limb of loop of Henle from reabsorbing NaCl Glycerin, isosorbide, mannitol, and urea Often used for cerebral edema

8 Diuretic Groups (cont d) Carbonic anhydrase inhibitors Work within proximal tubule Decrease HCO 3- and NaCl reabsorption Net result: Moderate NaCl increase plus water excretion Weak action plus potential for metabolic acidosis Hypokalemia is common adverse effect

9 Diuretic Groups (cont d) Loop diuretics Furosemide, bumetanide, torsemide Inhibit NaCl reabsorption at ascending limb of loop of Henle High-ceiling diuretics Up to 20% of NaCl and H 2 O lost May cause acute vasodilation Larger doses required with renal dysfunction

10 Diuretic Groups (cont d) Thiazide diuretics Block NaCl reabsorption at distal tubule First-line treatment for mild hypertension (HTN) Narrow therapeutic margin May also decrease peripheral vascular resistance

11 Diuretic Groups (cont d) Potassium-sparing diuretics Block exchange of Na for K and H Weak action May cause hyperkalemia Spironolactone Competitive aldosterone antagonist Common in cirrhosis and ascites

12 Diuretic Groups (cont d) Potassium-sparing diuretics (cont d) Triamterene Blocks Na channels in collecting ducts Short-acting Metabolized by liver Amiloride Blocks Na channels in collecting ducts Moderately long half-life

13 Diuretic Combinations May produce additive or synergistic effect Most common is loop diuretic plus thiazide

14 Drug Interactions

15 Adverse Effects Hypovolemia Hypokalemia Acid-base disorders Glucose changes Ototoxicity

16 Other Considerations Not recommended during pregnancy/breastfeeding Side effects in children similar to adult May require smaller doses Furosemide is effective/least toxic in pediatric practice Loop diuretics may cause nephrocalcinosis